This proposal is a continuing effort designed to study the effect of chronic ethanol administration and ethanol withdrawal on the ultrastructural and cytochemical characteristics of glutamatergic synapses of the dentate fascia and hippocampus proper in lines of mice that were bred for differential sensitivity to ethanol: the Long-Sleep (LS) and Short-Sleep (SS) mice. During this grant period we have established that chronic ethanol consumption induces morphometric changes in synapses of the dentate fascia and hippocampus in the two lines of mice. The morphological changes include a decreased density of spines in the stratum oriens of CA1, an increased complexity of spines in the dentate molecular layer, an enlargement of mossy terminals and a decrease in the number of basket cells in the dentate fascia of the LS mice. However, all these parameters were unchanged in the SS mice. The ethanol induced increase of the mossy fiber terminals in the LS may be interpreted as a mechanism that compensates for the inhibitory effect of the drug in the ethanol sensitive LS mice, so that the flow of information through the hippocampus could be maintained. Similarly, the loss of GABAergic basket cells which are inhibitory interneurons in the hippocampus and the dentate fascia may be viewed as an adaptive mechanism protecting the ethanol sensitive LS mice against overt inhibition. In the proposed experiments synaptic parameters like the length of synaptic apposition and the vesicle density in the mossy terminals will be studied. Since mossy terminals are characterized by a high content of zinc which fluctuates with synaptic activation and is depleted during seizure activity, the Zn2+ content could serve as an indicator of the functional states of the mossy terminals. The Ca2+ content could serve a similar purpose. Thus, these cations will be studied in mossy terminals of both genotypes with and without ethanol exposure and during ethanol withdrawal. Since there is a good reason to believe that ethanol may affect the internal Ca2+ stores in the smooth endoplasmic reticulum and mitochondria, relative distribution of Ca2+ (in the form of Ca+-oxalate-pyroantimonate precipitates) between these compartments and the cytoplasm will be studied as well. Since ethanol is likely to exert an inhibitory effect on the hippocampus through the GABAergic system, the basket cells and their circuitry will be studied at the light and electron microscope levels through the use of the antiGAD antibodies.